6,250 research outputs found
Enhancement of bulk second-harmonic generation from silicon nitride films by material composition
We present a comprehensive tensorial characterization of second-harmonic
generation from silicon nitride films with varying composition. The samples
were fabricated using plasma-enhanced chemical vapor deposition, and the
material composition was varied by the reactive gas mixture in the process. We
found a six-fold enhancement between the lowest and highest second-order
susceptibility, with the highest value of approximately 5 pm/V from the most
silicon-rich sample. Moreover, the optical losses were found to be sufficiently
small (below 6 dB/cm) for applications. The tensorial results show that all
samples retain in-plane isotropy independent of silicon content, highlighting
the controllability of the fabrication process.Comment: 4 pages, 3 figures, 2 tables; Re-submitted to Optics Letter
Transition Metal Chemistry of Oxime Containing Ligands: Part III-Complexes of Fe(II), Co(II) & Ni(II) with Pyridine-2-aldoxime & 6-Methylpyridine-2-aldoxime
696-69
Phase stability and structural temperature dependence in sodium niobate: A high resolution powder neutron diffraction study
We report investigation of structural phase transitions in technologically
important material sodium niobate as a function of temperature on heating over
300-1075 K. Our high resolution powder neutron diffraction data show variety of
structural phase transitions ranging from non-polar antiferrodistortive to
ferroelectric and antiferroelectric in nature. Discontinuous jump in lattice
parameters is found only at 633 K that indicates that the transition of
orthorhombic antiferroelectric P (space group Pbcm) to R (space group Pbnm)
phase is first order in nature, while other successive phase transitions are of
second order. New superlattice reflections appear at 680 K (R phase) and 770 K
(S phase) that could be indexed using an intermediate long-period modulated
orthorhombic structure whose lattice parameter along direction is 3 and 6
times that of the CaTiO3-like Pbnm structure respectively. The correlation of
superlattice reflections with the phonon instability is discussed. The critical
exponent ({\beta}) for the second order tetragonal to cubic phase transition at
950 K, corresponds to a value {\beta}, as obtained from the
temperature variation of order parameters (tilt angle and intensity of
superlattice reflections). It is argued that this exponent is due to a second
order phase transition close to a tricritical point. Based on our detailed
temperature dependent neutron diffraction studies, the phase diagram of sodium
niobate is presented that resolves existing ambiguities in the literature.Comment: 21 Pages, 8 Figure
Aggregation number distributions and mesoglobules in dilute solutions of diblock and triblock copolymers
We investigate the aggregation number and size distributions for
inter-molecular clusters of amphiphilic diblock and triblock copolymers in poor
solvent at very low concentrations. Diblocks and triblocks with hydrophilic
ends are shown to possess narrow distributions corresponding to formation of
monodispersed mesoglobules. Diblocks with hydrophobic ends are found to produce
inter-cluster multimers due to bridging by the hydrophilic middle blocks,
resulting in polydisperse distributions. Implications of these observations for
preparation of monodispersed nanoparticles and, potentially, understanding of
the quaternary structure of proteins are discussed.Comment: 4 pages, 4 PS figures. Accepted for publication in EP
Synchrotron X-ray Diffraction Study of BaFe2As2 and CaFe2As2 at High Pressures up to 56 GPa: Ambient and Low-Temperatures Down to 33 K
We report high pressure powder synchrotron x-ray diffraction studies on
MFe2As2 (M=Ba, Ca) over a range of temperatures and pressures up to about 56
GPa using a membrane diamond anvil cell. A phase transition to a collapsed
tetragonal phase is observed in both compounds upon compression. However, at
300 (33) K in the Ba-compound the transition occurs at 26 (29) GPa, which is a
much higher pressure than 1.7 (0.3) GPa at 300 (40) K in the Ca-compound, due
to its larger volume. It is important to note that the transition in both
compounds occurs when they are compressed to almost the same value of the unit
cell volume and attain similar ct/at ratios. We also show that the FeAs4
tetrahedra are much less compressible and more distorted in the collapsed
tetragonal phase than their nearly regular shape in the ambient pressure phase.
We present a detailed analysis of the pressure dependence of the structures as
well as equation of states in these important BaFe2As2 and CaFe2As2 compounds.Comment: 26 pages, 12 figure
DeepBus: Machine Learning based Real Time Pothole Detection System for Smart Transportation using IoT
Road related accidents have always been a nuisance to drivers and pedestrians alike. Every year countless accidents and deaths occur due to potholes which could have been preventable if there had been a prior warning or if the civic authorities were able to repair these potholes in time. This paper proposes a machine learning based pothole detection system called DeepBus for real time identification of surface irregularities on roads using Internet of Things (IoT). DeepBus uses IoT sensors to detect potholes in real time while an end user is driving vehicles on the road. The location of these potholeswould be available on a centrally hosted map which can be accessed by both end users and civic authorities. Thus, it would serve as a warning system to all users as well as a database of potholes with thier locations to the authorities for quick repair and action. We have compared the performance of various machine learning models (Logistic Regression, Support Vector Machine (SVM), K‐Nearest Neighbors (KNN), Naive Bayes, Decision Tree, Random Forest and Ensemble Voting) based on different parameters (Accuracy, F‐score, Precision and Recall) and identified that Random Forest is the best model for pothole detection
Agricultural innovation and adaptation to climate change: empirical evidence from diverse agro-ecologies in South Asia
While impacts of climate change on agricultural systems have been widely researched, there is still limited understanding of what agricultural practices evolves over time in response to both climatic and non-climatic drivers and how actors mobilize their resources, institutions and practices in South Asia. Through eight case studies and a survey of300 households in 15 locations in India, Nepal and Bangladesh, this paper generates empirical evidence on emerging agricultural interventions in contrasting socio-economic, geographical and agro-ecological contexts. The study shows that several farm practices emerge out in response to multiple drivers over time; some of them can be further adjusted to the challenge of climate change by planned adaptation programs. Most actors, however, have considered private risks in the short run. Although there has been some progress in streamlining climate change into strategic planning in different countries of South Asia, policy, research and extension systems lack adequate attention to wider resilience of the system. Based on this analysis, we recommend that adaptation policies should complement farmers’ responses to climate change through informed research and extension systems and pro-poor government policies that improve adaptation and coordinate activities of different actors
Magnetic Lattice Dynamics of the Oxygen-Free FeAs Pnictides: How Sensitive are Phonons to Magnetic Ordering?
To shed light on the role of magnetism on the superconducting mechanism of
the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering
on phonon dynamics in the low-temperature orthorhombic parent compounds, which
present a spin-density wave. The study covers both the 122 (AFe2As2; A=Ca, Sr,
Ba) and 1111 (AFeAsF; A=Ca, Sr) phases. We extend our recent work on the Ca
(122 and 1111) and Ba (122) cases by treating computationally and
experimentally the 122 and 1111 Sr compounds. The effect of magnetic ordering
is investigated through detailed non-magnetic and magnetic lattice dynamical
calculations. The comparison of the experimental and calculated phonon spectra
shows that the magnetic interactions/ordering have to be included in order to
reproduce well the measured density of states. This highlights a
spin-correlated phonon behavior which is more pronounced than the apparently
weak electron-phonon coupling estimated in these materials. Furthermore, there
is no noticeable difference between phonon spectra of the 122 Ba and Sr,
whereas there are substantial differences when comparing these to CaFe2As2
originating from different aspects of structure and bonding
Optical control of in-plane domain configuration and domain wall motion in ferroelectric and ferroelastic
The sensitivity of ferroelectric domain walls to external stimuli makes them
functional entities in nanoelectronic devices. Specifically, optically driven
domain reconfiguration with in-plane polarization is advantageous and thus
highly sought. Here, we show the existence of in-plane polarized sub-domains
imitating a single domain state and reversible optical control of its domain
wall movement in a single-crystal of ferroelectric BaTiO3. Similar optical
control in the domain configuration of non-polar ferroelastic material
indicates long-range ferroelectric polarization is not essential for the
optical control of domain wall movement. Instead, flexoelectricity is found to
be an essential ingredient for the optical control of the domain configuration
and hence, ferroelastic materials would be another possible candidate for
nanoelectronic device applications
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